/HI,
The Avast File Shredder/Data Shredder - clean drive - has caused me a lot of problems. Fortunately, with the help of the internet, I was able to find a solution.
The data shredder reduced my hard drive space of 130gb to 500mb on 4/29/2016 - See 5/1/2016 text file.
Then after I found the issue, I choose to do it again thinking the reason I had the issue was that of the lack of hard drive space - it reduced my hard drive from 296gb to 0gb overnight.
In both of these situations, the Avast Data Shredder was at 93%, and nothing was happening so I stopped it.
I have used other shredders before with no issues.
Avast support has denied there is an issue with the software.
I hope someone from Avast would take a good look at the problem and find a solution.
CCleaner Data Analyzer was a great help in finding the large data files which were hidden.